In the printing and duplicating field there are various applications where a copy sheet printed on a first surface by a first printing couple is advanced to a second printing couple for printing on the other surface.
While applications such as the foregoing have been normally handled heretofore by arranging the printing couples in straight-line tandem, such tandem arrangements impose certain limitations which restrict the use of the equipment to specific applications. Thus, when the printing couples are arranged in tandem, the overall size of the combined units is extended considerably thereby requiring substantial floor space and precluding the use of such equipment in very small size work areas. Also, when the units are arranged in tandem the machine operator does not have ready access and is not within easy reach of the units and the controls therefor to perform any operations or adjustments that might be required during machine operation.
Furthermore when the printing couples are arranged in tandem, the customary turn-over devices available cause the copy sheets to be turned end-over-end with the result that (1) the master must be placed on the second printing couple in a position reversed with respect to the position of the master on the first printing couple, and (2) the registration of the impressions on the second surfaces of the copy sheets with those on the first surfaces presents a difficult problem in view of the fact that the edge of the sheet used for registration of the impression is the top edge in one case and the bottom edge in the other.